The invention relates generally to a lip seal for a piston. More particularly, the invention relates to a piston with a lip seal for use in a dispensing cartridge, as well as dispensing systems with cartridges using such pistons.
Fluid cartridges used in adhesive and sealant dispensing systems typically include one or more pistons that form a seal with an inner wall of an axial bore of the cartridge. After the cartridge has been initially filled with adhesive/sealant, the piston is positioned near a back wall of the cartridge. To expel the adhesive/sealant through an outlet in a front wall of the cartridge, a dispenser, such as caulking gun or the like, is coupled with the piston and used to advance the piston along the axial bore toward the outlet.
One of the challenges associated with such pistons relates to maintaining the seal with the inner wall of the cartridge. For example, many pistons include a central body and a sealing lip extending from the central body. The sealing lip is generally an outer wall sized to create an interference fit with the cartridge to form the seal. Because the sealing lip extends outwardly from the central body at an angle, the seal is primarily formed by a terminal end of the sealing lip. The terminal end includes a well-defined peripheral edge that contacts the inner wall of the cartridge.
Conventional sealing lips are prone to leakage. Prior to insertion into the cartridge, the peripheral edge of the sealing lip may be nicked or scratched during transport, handling, or the like. Additionally, the peripheral edge is often formed at a parting line of the mold pieces used to manufacture the piston and, therefore, is susceptible to “flash” (occurs when excess material penetrates the parting line and remains attached to the peripheral edge). Such manufacturing defects and damage to the peripheral edge (or the terminal end in general) may compromise the ability of the piston to maintain a seal with the inner wall of the cartridge. In particular, after the piston is assembled in the cartridge and the cartridge is filled with material and stored, the material may flow through the nicks or scratches and past the piston. Additional leakage past the piston may occur during dispensing operations as the piston moves toward the outlet and pressurizes the fluid. This undesirable leakage, which is referred to as “blow-by,” may result in the material flowing onto portions of the dispenser or into other unintended areas.
Some manufacturers have attempted to increase the reliability of piston sealing lips by providing a rounded or chamfered edge at the terminal end. Although design modifications may make the edge more robust and less susceptible to damage, the modifications may have a tendency to promote blow-by during dispensing operations. This is because rounded and chamfered edges make it easier for material to flow past the sealing lip. Thus, the design modifications that make the edge more robust may also make the edge less effective at maintaining a seal during dispensing operations.
Therefore, a piston with a sealing lip design configured to reduce or minimize blow-by and other leakage is highly desirable.